Active heat sink

ABSTRACT

A system including a cooling element and a support structure is described. The cooling element has a first side and a second side opposite to the first side. The cooling element is configured to undergo vibrational motion when actuated to drive a fluid from the first side to the second side. The support structure thermally couples the cooling element to a heat-generating structure via thermal conduction.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/486,747 entitled ACTIVE HEAT SINK filed Sep. 27, 2021, which claimspriority to U.S. Provisional Patent Application No. 63/087,002 entitledACTIVE HEAT SINK filed Oct. 2, 2020, both of which are incorporatedherein by reference for all purposes.

BACKGROUND OF THE INVENTION

As computing devices grow in speed and computing power, the heatgenerated by the computing devices also increases. Various mechanismshave been proposed to address the generation of heat. Active devices,such as fans, may be used to drive air through large computing devices,such as laptop computers or desktop computers. Passive cooling devices,such as heat spreaders, may be used in smaller, mobile computingdevices, such as smartphones, virtual reality devices and tabletcomputers. However, such active and passive devices may be unable toadequately cool both mobile devices such as smartphones and largerdevices such as laptops and desktop computers. Consequently, additionalcooling solutions for computing devices are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIGS. 1A-1F depict embodiments of active cooling systems includingactive heat sinks.

FIGS. 2A-2G depict an indication of fluid temperature in active heatsinks.

FIGS. 3A-3D depict embodiments of actuators usable in active coolingsystems including centrally anchored cooling elements.

FIG. 4 depicts an embodiment of an active cooling system including anactive heat sink.

FIG. 5 depicts an embodiment of an active cooling system including anactive heat sink.

FIG. 6 depicts an embodiment of an active cooling system including anactive heat sink.

FIG. 7 depicts an embodiment of an active cooling system including anactive heat sink.

FIG. 8 depicts an embodiment of an active cooling system including anactive heat sink.

FIG. 9 depicts an embodiment of an active cooling system including anactive heat sink.

FIGS. 10A-10B depict an embodiment of an active cooling system includingmultiple cooling cells configured as a tile and including active heatsinks.

FIG. 11 depicts an embodiment of an active cooling system includingmultiple cooling cells having active heat sinks.

FIG. 12 is a flow chart depicting an embodiment of a technique fordriving an active heat sink.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

As semiconductor devices become increasingly powerful, the heatgenerated during operations also grows. For example, processors formobile devices such as smartphones, tablet computers, notebooks, andvirtual reality devices can operate at high clock speeds, but produce asignificant amount of heat. Because of the quantity of heat produced,processors may run at full speed only for a relatively short period oftime. After this time expires, throttling (e.g. slowing of theprocessor's clock speed) occurs. Although throttling can reduce heatgeneration, it also adversely affects processor speed and, therefore,the performance of devices using the processors. As technology moves to5G and beyond, this issue is expected to be exacerbated.

Larger devices, such as laptop or desktop computers include electricfans that have rotating blades. The fan that can be energized inresponse to an increase in temperature of internal components. The fansdrive air through the larger devices to cool internal components.However, such fans are typically too large for mobile devices such assmartphones or for thinner devices such as tablet computers. Fans alsomay have limited efficacy because of the boundary layer of air existingat the surface of the components, provide a limited airspeed for airflow across the hot surface desired to be cooled and may generate anexcessive amount of noise. Passive cooling solutions may includecomponents such as a heat spreader and a heat pipe or vapor chamber totransfer heat to a heat exchanger. Although a heat spreader somewhatmitigates the temperature increase at hot spots, the amount of heatproduced in current and future devices may not be adequately addressed.Similarly, a heat pipe or vapor chamber may provide an insufficientamount of heat transfer to remove excessive heat generated.

Varying configurations of computing devices further complicate heatmanagement. For example, computing devices such as laptops arefrequently open to the external environment while other computingdevices, such as smartphones, are generally closed to the externalenvironment. Thus, active heat management solutions for open devices,such as fans, may be inappropriate for closed devices. A fan drivingheated fluid from the inside of the computing device to the outsideenvironment may be too large for closed computing devices such assmartphones and may provide limited fluid flow. In addition, the closedcomputing device has no outlet for the heated fluid even if the fan canbe incorporated into the closed computing device. Thus, the thermalmanagement provided by such an open-device mechanism may have limitedefficacy. Even for open computing devices, the location of the inletand/or outlet may be configured differently for different devices. Forexample, an outlet for fan-driven fluid flow in a laptop may be desiredto be located away from the user's hands or other structures that maylie within the outflow of heated fluid. Such a configuration not onlyprevents the user's discomfort but also allows the fan to provide thedesired cooling. Another mobile device having a different configurationmay require the inlets and/or outlets to be configured differently, mayreduce the efficacy of such heat management systems and may prevent theuse of such heat management systems. Thus, mechanisms for improvingcooling in computing devices are desired.

Similarly, servers, batteries, automotive components, some mobiledevices and other technologies that typically used for longer periods oftime are desired to be cooled. For such technologies, heat generatedduring steady state operation of the device may be a larger concern.Thus steady state cooling solutions are also desired.

A system including a cooling element and a support structure isdescribed. The cooling element has a first side and a second sideopposite to the first side. The cooling element is configured to undergovibrational motion when actuated to drive a fluid from the first side tothe second side. The support structure thermally couples the coolingelement to a heat-generating structure via thermal conduction. In someembodiments, the support structure further includes a bottom plate andsidewalls forming a chamber therein. The cooling element is in thechamber. The bottom plate and/or the sidewalls have orifices therein.The cooling element is actuated to drive the fluid through the orifices.The vibrational motion of the cooling element may drive the fluid suchthat the fluid exiting the orifices has a speed of at least thirtymeters per second. The support structure may also include a top platehaving vent(s) therein. The cooling element is between the top plate andthe heat-generating structure. Thus, a top chamber is formed between thecooling element and the top plate and a bottom chamber is formed betweenthe cooling element and the bottom plate. The cooling element may have acentral region and a perimeter. The support structure may furtherinclude an anchor configured to support the cooling element at thecentral region. At least a portion of the perimeter is free to undergothe vibrational motion.

In some embodiments, the system includes a heat spreader integrated withthe support structure. The heat spreader is thermally coupled to thesupport structure and the heat-generating structure via thermalconduction. In some embodiments, the support structure is configuredsuch that the fluid exiting at least a portion of the orifices impingeson the heat spreader to extract heat from the heat spreader. The heatspreader extracting heat from the heat-generating structure via thermalconduction. The cooling element may be configured such that the fluiddriven by the vibrational motion extracts heat from the cooling element.In some embodiments, the support structure includes a pedestal thermallyconductively coupled to the heat-generating structure. Theheat-generating structure may be is selected from an integrated circuit,a battery, a heat spreader, and a vapor chamber.

An active heat sink is described. The active heat sink includes multiplecooling cells and a support structure. Each of the cooling cellsincludes a cooling element, a top plate having at least one venttherein, a bottom plate, sidewalls forming a chamber therein, and ananchor. The cooling element is in the chamber between the top plate andthe bottom plate. The bottom plate and/or the sidewalls have orificestherein. The cooling element is actuated to undergo vibrational motionto drive a fluid through the orifices. The support structure isintegrated with the cooling cells and thermally couples the coolingelement to a heat-generating structure via thermal conduction.

In some embodiments, the cooling element has a central region and aperimeter. In such embodiments, the support structure further includesan anchor for each of the cooling elements. The anchor is configured tosupport the cooling element at the central region. At least a portion ofthe perimeter is free to undergo the vibrational motion. In someembodiments, the active heat sink includes a heat spreader integratedwith the support structure. The heat spreader is thermally coupled tothe support structure and the heat-generating structure via thermalconduction. The cooling element may be configured such that the fluiddriven by the vibrational motion extracts heat from the cooling element.In some embodiments, the support structure further includes a pedestalthermally conductively connecting the heat-generating structure. In someembodiments, the heat-generating structure is selected from anintegrated circuit, a battery, a heat spreader, and a vapor chamber.

A method of cooling a heat-generating structure is described. The methodincludes driving a cooling element to induce a vibrational motion at afrequency. The cooling element has a first side and a second sideopposite to the first side. The cooling element is configured to undergovibrational motion when actuated to drive a fluid from the first side tothe second side. The cooling element is thermally coupled by a supportstructure to the heat-generating structure. The support structurethermally couples the cooling element to the heat-generating structurevia thermal conduction. In some embodiments, the frequency correspondsto a structural resonance for the cooling element and to an acousticresonance for at least a portion of a chamber in which the coolingelement resides. In some embodiments, the cooling element is one of aplurality of cooling elements. In such embodiments, driving the coolingelement further includes driving the plurality of cooling elements toinduce the vibrational motion in each of the cooling elements. Each ofthe cooling elements is thermally coupled to the heat-generatingstructure via thermal conduction. In some embodiments, a heat spreaderis integrated with the support structure. The heat spreader is thermallycoupled to the heat-generating structure.

FIGS. 1A-1F are diagrams depicting exemplary embodiments of activecooling systems 100 and 100′ usable with heat-generating structure 102and forming an active heat sink. For clarity, only certain componentsare shown. FIGS. 1A-1F are not to scale. Although shown as symmetric,cooling system(s) 100 and/or 100′ need not be. FIGS. 1A-1E depictvarious modes of one embodiment of a cooling system. FIG. 1F depictsanother embodiment of a cooling system 100′.

Cooling system 100 includes cooling element 120 and support structure170. In the embodiment shown in FIGS. 1A-1E, support structure 170includes top plate 110 having vent 112 therein, orifice plate 130 havingorifices 132 therein, anchor 160, pedestal 172 and sidewalls 174.Cooling element 120 divides the interior of support structure 170 intotop chamber 140 and bottom chamber 150. Chambers 140 and 150(collectively chamber 140/150) are formed within orifice, or bottom,plate 130, top plate 110 and sidewalls 174. Support structure 170 isthermally coupled to heat-generating structure 102 via pedestal 172.Pedestal 172 also provides a space for fluid to flow between orificeplate 130 and heat-generating structure 102 (i.e. a jet channel). Insome embodiments, heat-generating structure 102 is separate from coolingsystem 100. In some embodiments, heat-generating structure 102 may beintegrated into support structure 170. In such embodiments,heat-generating structure 102 may be a heat spreader that is thermallyand mechanically coupled to cooling element 120 via pedestal 172,orifice plate 130, and anchor 160. Thus, heat-generating structure (i.e.heat spreader) 102 extracts heat from integrated circuit 103 (or otherstructure that generates heat) via conduction. This heat may betransferred to other portions of cooling system 100 through pedestal 172via conduction.

Cooling element 120 is supported at its central region by anchor 160.Regions of cooling element 120 closer to and including portions of thecooling element's perimeter (e.g. tip 123) vibrate when actuated. Insome embodiments, tip 123 of cooling element 120 includes a portion ofthe perimeter furthest from anchor 160 and undergoes the largestdeflection during actuation of cooling element 120. For clarity, onlyone tip 123 of cooling element 120 is labeled in FIG. 1A.

FIG. 1A depicts cooling system 100 in a neutral position. Thus, coolingelement 120 is shown as substantially flat. For in-phase operation,cooling element 120 is driven to vibrate between positions shown inFIGS. 1B and 1C. This vibrational motion draws fluid (e.g. air) intovent 112, through chambers 140 and 150 and out orifices 132 at highspeed and/or flow rates. For example, the speed at which the fluidimpinges on heat-generating structure 102 may be at least thirty metersper second. In some embodiments, the fluid is driven by cooling element120 toward heat-generating structure 102 at a speed of at leastforty-five meters per second. In some embodiments, the fluid is driventoward heat-generating structure 102 by cooling element 120 at speeds ofat least sixty meters per second. Other speeds may be possible in someembodiments. Cooling system 100 is also configured so that little or nofluid is drawn back into chamber 140/150 through orifices 132 by thevibrational motion of cooling element 120.

In the embodiment shown, heat-generating structure 102 is a heatspreader or vapor chamber thermally connected to integrated circuit 103.Thus, integrated circuit 103 generates heat, which is transferred toheat-generating structure (i.e. heat spreader) 102. Thus, integratedcircuit 103 may also be considered to be a heat-generating structure. Inthe embodiment shown, the heat is transferred between integrated circuit103 and heat spreader 102 via conduction. In some embodiments, anadditional structure may be interposed between heat-generating structure102 and integrated circuit 103. For example, an additional heat spreaderand/or a vapor chamber may be present. Because cooling system 100 isthermally coupled to and cools structure 102, structure 102 is describedas a heat-generating structure. However, in the embodiment shown,cooling of heat-generating structure 102 is a mechanism for managingheat produced by integrated circuit 103. In some embodiments,heat-generating structure 102 generates heat. For example,heat-generating structure 102 may be an integrated circuit, such asintegrated circuit 103. Such an embodiment may be viewed as omittingheat-generating structure 102 or omitting integrated circuit 103. Insome embodiments, heat-generating structure 102 is desired to be cooledbut does not generate heat itself. Heat-generating structure 102 mayconduct heat (e.g. from a nearby object that generates heat such asintegrated circuit 103). Thus, heat-generating structure 102 might be aheat spreader or a vapor chamber as shown in FIGS. 1A-1F. In some suchembodiments, heat-generating structure 102 may be a thermally conductivepart of a module containing cooling system 100. For example, coolingsystem 100 may be affixed to heat-generating structure 102, which may becoupled to another heat sink, vapor chamber, integrated circuit 103, orother separate structure desired to be cooled. Although described in thecontext of integrated circuit 103, cooling system 100 may be used tocool another component or device. For example, heat-generating structure102 or integrated circuit 103 may include or be replaced by othersemiconductor components(s) including individual integrated circuitcomponents such as processors, other integrated circuit(s) and/or chippackage(s); sensor(s); optical device(s); one or more batteries; othercomponent(s) of an electronic device such as a computing device; heatspreaders; heat pipes; other electronic component(s) and/or otherdevice(s) desired to be cooled.

The devices in which cooling system 100 is desired to be used may alsohave limited space in which to place a cooling system. For example,cooling system 100 may be used in computing devices. Such computingdevices may include but are not limited to smartphones, tabletcomputers, laptop computers, tablets, two-in-one laptops, hand heldgaming systems, digital cameras, virtual reality headsets, augmentedreality headsets, mixed reality headsets and other devices that arethin. Cooling system 100 may be a micro-electro-mechanical system (MEMS)cooling system capable of residing within mobile computing devicesand/or other devices having limited space in at least one dimension. Forexample, the total height of cooling system 100 (from the top ofheat-generating structure 102 to the top of top plate 110) may be lessthan 2 millimeters. In some embodiments, the total height of coolingsystem 100 is not more than 1.5 millimeters. In some embodiments, thistotal height is not more than 1.1 millimeters. In some embodiments, thetotal height does not exceed one millimeter. In some embodiments, thetotal height does not exceed two hundred and fifty micrometers.Similarly, the distance between the bottom of orifice plate 130 and thetop of heat-generating structure 102, y, may be small. In someembodiments, y is at least two hundred micrometers and not more than onemillimeter. In some embodiments, y is at least two hundred micrometersand not more than three hundred micrometers. Thus, cooling system 100 isusable in computing devices and/or other devices having limited space inat least one dimension. However, nothing prevents the use of coolingsystem 100 in devices having fewer limitations on space and/or forpurposes other than cooling. Although one cooling system 100 is shown(e.g. one cooling cell), multiple cooling systems 100 might be used inconnection with heat-generating structure 102. For example, a one ortwo-dimensional array of cooling cells might be utilized.

Cooling system 100 is in communication with a fluid used to coolheat-generating structure 102. The fluid may be a gas or a liquid. Forexample, the fluid may be air. In some embodiments, the fluid includesfluid from outside of the device in which cooling system 100 resides(e.g. provided through external vents in the device). In someembodiments, the fluid circulates within the device in which coolingsystem resides (e.g. in an enclosed device).

Cooling element 120 can be considered to divide the interior of activecooling system 100 into top chamber 140 and bottom chamber 150. Topchamber 140 is formed by cooling element 120, the sides, and top plate110. Bottom chamber 150 is formed by orifice plate 130, the sides,cooling element 120 and anchor 160. Top chamber 140 and bottom chamber150 are connected at the periphery of cooling element 120 and togetherform chamber 140/150 (e.g. an interior chamber of cooling system 100).

The size and configuration of top chamber 140 may be a function of thecell (cooling system 100) dimensions, cooling element 120 motion, andthe frequency of operation. Top chamber 140 has a height, h1. The heightof top chamber 140 may be selected to provide sufficient pressure todrive the fluid to bottom chamber 150 and through orifices 132 at thedesired flow rate and/or speed. Top chamber 140 is also sufficientlytall that cooling element 120 does not contact top plate 110 whenactuated. In some embodiments, the height of top chamber 140 is at leastfifty micrometers and not more than five hundred micrometers. In someembodiments, top chamber 140 has a height of at least two hundred andnot more than three hundred micrometers.

Bottom chamber 150 has a height, h2. In some embodiments, the height ofbottom chamber 150 is sufficient to accommodate the motion of coolingelement 120. Thus, no portion of cooling element 120 contacts orificeplate 130 during normal operation. Bottom chamber 150 is generallysmaller than top chamber 140 and may aid in reducing the backflow offluid into orifices 132. In some embodiments, the height of bottomchamber 150 is the maximum deflection of cooling element 120 plus atleast five micrometers and not more than ten micrometers. In someembodiments, the deflection of cooling element 120 (e.g. the deflectionof tip 123), z, has an amplitude of at least ten micrometers and notmore than one hundred micrometers. In some such embodiments, theamplitude of deflection of cooling element 120 is at least tenmicrometers and not more than sixty micrometers. However, the amplitudeof deflection of cooling element 120 depends on factors such as thedesired flow rate through cooling system 100 and the configuration ofcooling system 100. Thus, the height of bottom chamber 150 generallydepends on the flow rate through and other components of cooling system100.

Top plate 110 includes vent 112 through which fluid may be drawn intocooling system 100. Top vent 112 may have a size chosen based on thedesired acoustic pressure in chamber 140. For example, in someembodiments, the width, w, of vent 112 is at least five hundredmicrometers and not more than one thousand micrometers. In someembodiments, the width of vent 112 is at least two hundred fiftymicrometers and not more than two thousand micrometers. In theembodiment shown, vent 112 is a centrally located aperture in top plate110. In other embodiments, vent 112 may be located elsewhere. Forexample, vent 112 may be closer to one of the edges of top plate 110.Vent 112 may have a circular, rectangular or other shaped footprint.Although a single vent 112 is shown, multiple vents might be used. Forexample, vents may be offset toward the edges of top chamber 140 or belocated on the side(s) of top chamber 140. Although top plate 110 isshown as substantially flat, in some embodiments trenches and/or otherstructures may be provided in top plate 110 to modify the configurationof top chamber 140 and/or the region above top plate 110.

Cooling element 120 includes an anchored region 122 and cantileveredarms 121. For simplicity, anchored region 122 and cantilevered arms 121are only labeled in FIGS. 1A and 1F. Anchored region 122 is supported(e.g. held in place) in cooling system 100 by anchor 160. Cantileveredarms 121 undergo vibrational motion in response to cooling element 120being actuated. In the embodiment shown in FIGS. 1A-1F, anchored region122 is centrally located along an axis of cooling elements 120 and 120′.In other embodiments, anchored region 122 may be at one edge of theactuator and outer region 128 at the opposing edge. In such embodiments,cooling element 120 is edge anchored. Although depicted as having auniform thickness, in some embodiments, cooling element 120 may have avarying thickness. For example, cooling element 120 may be replaced bycooling element 120′, discussed below.

Anchor 160 supports cooling element 120 at the central portion ofcooling element 120. Thus, at least part of the perimeter of coolingelement 120 is unpinned and free to vibrate. In some embodiments, anchor160 extends along a central axis of cooling element 120 (e.g.perpendicular to the page in FIGS. 1A-1F). In such embodiments, portionsof cooling element 120 that vibrate (e.g. cantilevered arms 121including tip 123) move in a cantilevered fashion. Thus, cantileveredarms 121 of cooling element 120 may move in a manner analogous to thewings of a butterfly (i.e. in-phase) and/or analogous to a seesaw (i.e.out-of-phase). Thus, the cantilevered arms 121 of cooling element 120that vibrate in a cantilevered fashion do so in-phase in someembodiments and out-of-phase in other embodiments. In some embodiments,anchor 160 does not extend along an axis of cooling element 120. In suchembodiments, all portions of the perimeter of cooling element 120 arefree to vibrate (e.g. analogous to a jellyfish). In the embodimentshown, anchor 160 supports cooling element 120 from the bottom ofcooling element 120. In other embodiments, anchor 160 may supportcooling element 120 in another manner. For example, anchor 160 maysupport cooling element 120 from the top (e.g. cooling element 120 hangsfrom anchor 160). Such an embodiment is shown and described in thecontext of FIG. 1F. In some embodiments, the width, a, of anchor 160 isat least 0.5 millimeters and not more than four millimeters. In someembodiments, the width of anchor 160 is at least two millimeters and notmore than 2.5 millimeters. Anchor 160 may occupy at least ten percentand not more than fifty percent of cooling element 120.

Cooling element 120 has a first side and a second side. In someembodiments, the first side is distal from heat-generating structure 102and the second side is proximate to heat-generating structure 102. Inthe embodiment shown in FIGS. 1A-1F, the first side of cooling element120 is the top of cooling element 120 (closer to top plate 110) and thesecond side is the bottom of cooling element 120 (closer to orificeplate 130). Cooling element 120 is actuated to undergo vibrationalmotion as shown in FIGS. 1A-1F. The vibrational motion of coolingelement 120 drives fluid from the first side of cooling element 120(e.g. distal from heat-generating structure 102/from top chamber 140) toa second side of cooling element 120 (e.g. proximate to heat-generatingstructure 102/to bottom chamber 150). The vibrational motion of coolingelement 120 draws fluid through vent 112 and into top chamber 140;forces fluid from top chamber 140 to bottom chamber 150; and drivesfluid from bottom chamber 150 through orifices 132 of orifice plate 130.Further, cooling element 120 and orifices 132 may be configured toreduce back flow of fluid from the jet channel into bottom chamber 150.Thus, cooling element 120 may be viewed as an actuator. Althoughdescribed in the context of a single, continuous cooling element, insome embodiments, cooling element 120 may be formed by two (or more)cooling elements. Each of the cooling elements has one portion pinned(e.g. supported by anchor 160) and an opposite portion unpinned. Thus, asingle, centrally supported cooling element 120 may be formed by acombination of multiple cooling elements supported at an edge.

Cooling element 120 has a length, L, that depends upon the frequency atwhich cooling element 120 is desired to vibrate. In some embodiments,the length of cooling element 120 is at least four millimeters and notmore than ten millimeters. In some such embodiments, cooling element 120has a length of at least six millimeters and not more than eightmillimeters. The depth of cooling element 120 (e.g. perpendicular to theplane shown in FIGS. 1A-1F) may vary from one fourth of L through twiceL. For example, cooling element 120 may have the same depth as length.The thickness, t, of cooling element 120 may vary based upon theconfiguration of cooling element 120 and/or the frequency at whichcooling element 120 is desired to be actuated. In some embodiments, thecooling element thickness is at least two hundred micrometers and notmore than three hundred and fifty micrometers for cooling element 120having a length of eight millimeters and driven at a frequency of atleast twenty kilohertz and not more than twenty-five kilohertz. Thelength, C of chamber 140/150 is close to the length, L, of coolingelement 120. For example, in some embodiments, the distance, d, betweenthe edge of cooling element 120 and the wall of chamber 140/50 is atleast one hundred micrometers and not more than five hundredmicrometers. In some embodiments, d is at least two hundred micrometersand not more than three hundred micrometers.

Cooling element 120 may be driven at a frequency that is at or near boththe resonant frequency for an acoustic resonance of a pressure wave ofthe fluid in top chamber 140 and the resonant frequency for a structuralresonance of cooling element 120. The portion of cooling element 120undergoing vibrational motion is driven at or near resonance (the“structural resonance”) of cooling element 120. This portion of coolingelement 120 undergoing vibration may be cantilevered arm(s) 121 in someembodiments. The frequency of vibration for structural resonance istermed the structural resonant frequency. Use of the structural resonantfrequency in driving cooling element 120 reduces the power consumptionof cooling system 100. Cooling element 120 and top chamber 140 may alsobe configured such that this structural resonant frequency correspondsto a resonance in a pressure wave in the fluid being driven through topchamber 140 (the acoustic resonance of top chamber 140). The frequencyof such a pressure wave is termed the acoustic resonant frequency. Atacoustic resonance, a node in pressure occurs near vent 112 and anantinode in pressure occurs near the periphery of cooling system 100(e.g. near tip 123 of cooling element 120 and near the connectionbetween top chamber 140 and bottom chamber 150). The distance betweenthese two regions is C/2. Thus, C/2=nλ/4, where λ is the acousticwavelength for the fluid and n is odd (e.g. n=1, 3, 5, etc.). For thelowest order mode, C=λ/2. Because the length of chamber 140 (e.g. C) isclose to the length of cooling element 120, in some embodiments, it isalso approximately true that L/2=nλ/4, where λ is the acousticwavelength for the fluid and n is odd. Thus, the frequency at whichcooling element 120 is driven, ν, is at or near the structural resonantfrequency for cooling element 120. The frequency ν is also at or nearthe acoustic resonant frequency for at least top chamber 140. Theacoustic resonant frequency of top chamber 140 generally varies lessdramatically with parameters such as temperature and size than thestructural resonant frequency of cooling element 120. Consequently, insome embodiments, cooling element 120 may be driven at (or closer to) astructural resonant frequency than to the acoustic resonant frequency.

Orifice plate 130 has orifices 132 therein. Although a particular numberand distribution of orifices 132 are shown, another number, otherlocation(s) and/or another distribution may be used. A single orificeplate 130 is used for a single cooling system 100. In other embodiments,multiple cooling systems 100 may share an orifice plate. For example,multiple cells 100 may be provided together in a desired configuration.In such embodiments, the cells 100 may be the same size andconfiguration or different size(s) and/or configuration(s). Orifices 132are shown as having an axis oriented normal to a surface ofheat-generating structure 102. In other embodiments, the axis of one ormore orifices 132 may be at another angle. For example, the angle of theaxis may be selected from substantially zero degrees and a nonzero acuteangle. Orifices 132 also have sidewalls that are substantially parallelto the normal to the surface of orifice plate 130. In some embodiments,orifices may have sidewalls at a nonzero angle to the normal to thesurface of orifice plate 130. For example, orifices 132 may becone-shaped. Further, although orifice place 130 is shown assubstantially flat, in some embodiments, trenches and/or otherstructures may be provided in orifice plate 130 to modify theconfiguration of bottom chamber 150 and/or the region between orificeplate 130 and heat-generating structure 102.

The size, distribution and locations of orifices 132 are chosen tocontrol the flow rate of fluid driven to the surface of heat-generatingstructure 102. The locations and configurations of orifices 132 may beconfigured to increase/maximize the fluid flow from bottom chamber 150through orifices 132 to the jet channel (the region between the bottomof orifice plate 130 and the top of heat-generating structure 102). Thelocations and configurations of orifices 132 may also be selected toreduce/minimize the suction flow (e.g. back flow) from the jet channelthrough orifices 132. For example, the locations of orifices are desiredto be sufficiently far from tip 123 that suction in the upstroke ofcooling element 120 (tip 123 moves away from orifice plate 13) thatwould pull fluid into bottom chamber 150 through orifices 132 isreduced. The locations of orifices are also desired to be sufficientlyclose to tip 123 that suction in the upstroke of cooling element 120also allows a higher pressure from top chamber 140 to push fluid fromtop chamber 140 into bottom chamber 150. In some embodiments, the ratioof the flow rate from top chamber 140 into bottom chamber 150 to theflow rate from the jet channel through orifices 132 in the upstroke (the“net flow ratio”) is greater than 2:1. In some embodiments, the net flowratio is at least 85:15. In some embodiments, the net flow ratio is atleast 90:10. In order to provide the desired pressure, flow rate,suction, and net flow ratio, orifices 132 are desired to be at least adistance, r1, from tip 123 and not more than a distance, r2, from tip123 of cooling element 120. In some embodiments r1 is at least onehundred micrometers (e.g. r1≥100 μm) and r2 is not more than onemillimeter (e.g. r2≤1000 μm). In some embodiments, orifices 132 are atleast two hundred micrometers from tip 123 of cooling element 120 (e.g.r1≥200 μm). In some such embodiments, orifices 132 are at least threehundred micrometers from tip 123 of cooling element 120 (e.g. r1≥300μm). In some embodiments, orifices 132 have a width of at least onehundred micrometers and not more than five hundred micrometers. In someembodiments, orifices 132 have a width of at least two hundredmicrometers and not more than three hundred micrometers. In someembodiments, the orifice separation, s, is at least one hundredmicrometers and not more than one millimeter. In some such embodiments,the orifice separation is at least four hundred micrometers and not morethan six hundred micrometers. In some embodiments, orifices 132 are alsodesired to occupy a particular fraction of the area of orifice plate130. For example, orifices 132 may cover at least five percent and notmore than fifteen percent of the footprint of orifice plate 130 in orderto achieve a desired flow rate of fluid through orifices 132. In someembodiments, orifices 132 cover at least eight percent and not more thantwelve percent of the footprint of orifice plate 130.

In some embodiments, cooling element 120 is actuated using apiezoelectric. Thus, cooling element 120 may be a piezoelectric coolingelement. Cooling element 120 may be driven by a piezoelectric that ismounted on or integrated into cooling element 120. In some embodiments,cooling element 120 is driven in another manner including but notlimited to providing a piezoelectric on another structure in coolingsystem 100. Cooling element 120 and analogous cooling elements arereferred to hereinafter as piezoelectric cooling element though it ispossible that a mechanism other than a piezoelectric might be used todrive the cooling element. In some embodiments, cooling element 120includes a piezoelectric layer on substrate. The substrate may includeor consist of stainless steel, a Ni alloy, Hastelloy, Al (e.g. an Alalloy), and/or a Ti (e.g. a Ti alloy such as Ti6A1-4V). In someembodiments, piezoelectric layer includes multiple sublayers formed asthin films on the substrate. In other embodiments, the piezoelectriclayer may be a bulk layer affixed to the substrate. Such a piezoelectriccooling element 120 also includes electrodes used to activate thepiezoelectric. The substrate functions as an electrode in someembodiments. In other embodiments, a bottom electrode may be providedbetween the substrate and the piezoelectric layer. Other layersincluding but not limited to seed, capping, passivation or other layersmight be included in piezoelectric cooling element. Thus, coolingelement 120 may be actuated using a piezoelectric.

In some embodiments, cooling system 100 includes chimneys (not shown) orother ducting. Such ducting provides a path for heated fluid to flowaway from heat-generating structure 102. In some embodiments, ductingreturns fluid to the side of top plate 110 distal from heat-generatingstructure 102. In some embodiments, ducting may instead direct fluidaway from heat-generating structure 102 in a direction parallel toheat-generating structure 102 or perpendicular to heat-generatingstructure 102 but in the opposite direction (e.g. toward the bottom ofthe page). For a device in which fluid external to the device is used incooling system 100, the ducting may channel the heated fluid to a vent.In such embodiments, additional fluid may be provided from an inletvent. In embodiments, in which the device is enclosed, the ducting mayprovide a circuitous path back to the region near vent 112 and distalfrom heat-generating structure 102. Such a path allows for the fluid todissipate heat before being reused to cool heat-generating structure102. In other embodiments, ducting may be omitted or configured inanother manner. Thus, the fluid is allowed to carry away heat fromheat-generating structure 102.

Operation of cooling system 100 is described in the context of FIGS.1A-1E. Although described in the context of particular pressures, gapsizes, and timing of flow, operation of cooling system 100 is notdependent upon the explanation herein. FIGS. 1B-1C depict in-phaseoperation of cooling system 100. Referring to FIG. 1B, cooling element120 has been actuated so that cantilevered arms 121 and tip 123 moveaway from top plate 110. FIG. 1B can thus be considered to depict theend of a down stroke of cooling element 120. Because of the vibrationalmotion of cooling element 120, gap 152 for bottom chamber 150 hasdecreased in size and is shown as gap 152B. Conversely, gap 142 for topchamber 140 has increased in size and is shown as gap 142B. During thedown stroke, a lower (e.g. minimum) pressure is developed at theperiphery when cooling element 120 is at the neutral position. As thedown stroke continues, bottom chamber 150 decreases in size and topchamber 140 increases in size as shown in FIG. 1B. Thus, fluid is drivenout of orifices 132 in a direction that is at or near perpendicular tothe surface of orifice plate 130 and/or the top surface ofheat-generating structure 102. The fluid is driven from orifices 132(toward heat-generating structure 102) at a high speed, for example inexcess of thirty-five meters per second. Thus, fluid exits orifices 132at the high speeds described herein. In some embodiments, the fluid thentravels along the surface of heat-generating structure 102 and towardthe periphery of heat-generating structure 102, where the pressure islower than near orifices 132. Also in the down stroke, top chamber 140increases in size and a lower pressure is present in top chamber 140. Asa result, fluid is drawn into top chamber 140 through vent 112. Themotion of the fluid into vent 112, through orifices 132, and along thesurface of heat-generating structure 102 is shown by unlabeled arrows inFIG. 1B.

Cooling element 120 is also actuated so that cantilevered arms 121 andthus tip 123 move away from heat-generating structure 102 and toward topplate 110. FIG. 1C can thus be considered to depict the end of an upstroke of cooling element 120. Because of the motion of cooling element120, gap 142 has decreased in size and is shown as gap 142C. Gap 152 hasincreased in size and is shown as gap 152C. During the upstroke, ahigher (e.g. maximum) pressure is developed at the periphery whencooling element 120 is at the neutral position. As the upstrokecontinues, bottom chamber 150 increases in size and top chamber 140decreases in size as shown in FIG. 1C. Thus, the fluid is driven fromtop chamber 140 (e.g. the periphery of chamber 140/150) to bottomchamber 150. Thus, when tip 123 of cooling element 120 moves up, topchamber 140 serves as a nozzle for the entering fluid to speed up and bedriven towards bottom chamber 150. The motion of the fluid into bottomchamber 150 is shown by unlabeled arrows in FIG. 1C. The location andconfiguration of cooling element 120 and orifices 132 are selected toreduce suction and, therefore, back flow of fluid from the jet channel(between heat-generating structure 102 and orifice plate 130) intoorifices 132 during the upstroke. Thus, cooling system 100 is able todrive fluid from top chamber 140 to bottom chamber 150 without an undueamount of backflow of heated fluid from the jet channel entering bottomchamber 140. Moreover, cooling system 100 may operate such that fluid isdrawn in through vent 112 and driven out through orifices 132 withoutcooling element 120 contacting top plate 110 or orifice plate 130. Thus,pressures are developed within chambers 140 and 150 that effectivelyopen and close vent 112 and orifices 132 such that fluid is driventhrough cooling system 100 as described herein.

The motion between the positions shown in FIGS. 1B and 1C is repeated.Thus, cooling element 120 undergoes vibrational motion indicated inFIGS. 1A-1C, drawing fluid through vent 112 from the distal side of topplate 110 into top chamber 140; transferring fluid from top chamber 140to bottom chamber 150; and pushing the fluid through orifices 132 andtoward heat-generating structure 102. As discussed above, coolingelement 120 is driven to vibrate at or near the structural resonantfrequency of cooling element 120. In some embodiments, this correspondsto the structural resonance of cantilevered arms 121. Further, thestructural resonant frequency of cooling element 120 is configured toalign with the acoustic resonance of the chamber 140/150. The structuraland acoustic resonant frequencies are generally chosen to be in theultrasonic range. For example, the vibrational motion of cooling element120 may be at frequencies from 15 kHz through 30 kHz. In someembodiments, cooling element 120 vibrates at a frequency/frequencies ofat least 20 kHz and not more than 30 kHz. The structural resonantfrequency of cooling element 120 is within ten percent of the acousticresonant frequency of cooling system 100. In some embodiments, thestructural resonant frequency of cooling element 120 is within fivepercent of the acoustic resonant frequency of cooling system 100. Insome embodiments, the structural resonant frequency of cooling element120 is within three percent of the acoustic resonant frequency ofcooling system 100. Consequently, efficiency and flow rate may beenhanced. However, other frequencies may be used.

Fluid driven toward heat-generating structure 102 may move substantiallynormal (perpendicular) to the top surface of heat-generating structure102. In some embodiments, the fluid motion may have a nonzero acuteangle with respect to the normal to the top surface of heat-generatingstructure 102. In either case, the fluid impinges on heat-generatingstructure 102 and may thin and/or form apertures in the boundary layerof fluid at heat-generating structure 102. As a result, transfer of heatfrom heat-generating structure 102 may be improved. The fluid deflectsoff of heat-generating structure 102, traveling along the surface ofheat-generating structure 102. In some embodiments, the fluid moves in adirection substantially parallel to the top of heat-generating structure102. Thus, heat from heat-generating structure 102 may be extracted bythe fluid. The fluid may exit the region between orifice plate 130 andheat-generating structure 102 at the edges of cooling system 100.Chimneys or other ducting (not shown) at the edges of cooling system 100allow fluid to be carried away from heat-generating structure 102. Inother embodiments, heated fluid may be transferred further fromheat-generating structure 102 in another manner. The fluid may exchangethe heat transferred from heat-generating structure 102 to anotherstructure or to the ambient environment. Thus, fluid at the distal sideof top plate 110 may remain relatively cool, allowing for the additionalextraction of heat. In some embodiments, fluid is circulated, returningto distal side of top plate 110 after cooling. In other embodiments,heated fluid is carried away and replaced by new fluid at the distalside of cooling element 120. As a result, heat-generating structure 102may be cooled.

FIGS. 1D-1E depict an embodiment of active cooling system 100 includingcentrally anchored cooling element 120 in which the cooling element isdriven out-of-phase. More specifically, cantilevered arms 121 of coolingelement 120 on opposite sides of anchor 160 (and thus on opposite sidesof the central, anchored region 122 of cooling element 120 that issupported by anchor 160) are driven to vibrate out-of-phase. In someembodiments, cantilevered arms 121 of cooling element 120 on oppositesides of anchor 160 are driven at or near one hundred and eighty degreesout-of-phase. Thus, one cantilevered arm 121 of cooling element 120vibrates toward top plate 110, while the other cantilevered arm 121 ofcooling element 120 vibrates toward orifice plate 130/heat-generatingstructure 102. Movement of a cantilevered arms 121 of cooling element120 toward top plate 110 (an upstroke) drives fluid in top chamber 140to bottom chamber 150 on that side of anchor 160. Movement of a sectionof cooling element 120 toward orifice plate 130 drives fluid throughorifices 132 and toward heat-generating structure 102. Thus, fluidtraveling at high speeds (e.g. speeds described with respect to in-phaseoperation) is alternately driven out of orifices 132 on opposing sidesof anchor 160. The movement of fluid is shown by unlabeled arrows inFIGS. 1D and 1E.

The motion between the positions shown in FIGS. 1D and 1E is repeated.Thus, cooling element 120 undergoes vibrational motion indicated inFIGS. 1A, 1D, and 1E, alternately drawing fluid through vent 112 fromthe distal side of top plate 110 into top chamber 140 for each side ofcooling element 120; transferring fluid from each side of top chamber140 to the corresponding side of bottom chamber 150; and pushing thefluid through orifices 132 on each side of anchor 160 and towardheat-generating structure 102. As discussed above, cooling element 120is driven to vibrate at or near the structural resonant frequency ofcooling element 120. Further, the structural resonant frequency ofcooling element 120 is configured to align with the acoustic resonanceof the chamber 140/150. The structural and acoustic resonant frequenciesare generally chosen to be in the ultrasonic range. For example, thevibrational motion of cooling element 120 may be at the frequenciesdescribed for in-phase vibration. The structural resonant frequency ofcooling element 120 is within ten percent of the acoustic resonantfrequency of cooling system 100. In some embodiments, the structuralresonant frequency of cooling element 120 is within five percent of theacoustic resonant frequency of cooling system 100. In some embodiments,the structural resonant frequency of cooling element 120 is within threepercent of the acoustic resonant frequency of cooling system 100.Consequently, efficiency and flow rate may be enhanced. However, otherfrequencies may be used.

Fluid driven toward heat-generating structure 102 for out-of-phasevibration may move substantially normal (perpendicular) to the topsurface of heat-generating structure 102, in a manner analogous to thatdescribed above for in-phase operation. Similarly, chimneys or otherducting (not shown) at the edges of cooling system 100 allow fluid to becarried away from heat-generating structure 102. In other embodiments,heated fluid may be transferred further from heat-generating structure102 in another manner. The fluid may exchange the heat transferred fromheat-generating structure 102 to another structure or to the ambientenvironment. Thus, fluid at the distal side of top plate 110 may remainrelatively cool, allowing for the additional extraction of heat. In someembodiments, fluid is circulated, returning to distal side of top plate110 after cooling. In other embodiments, heated fluid is carried awayand replaced by new fluid at the distal side of cooling element 120. Asa result, heat-generating structure 102 may be cooled.

Using the cooling system 100 actuated for in-phase vibration orout-of-phase vibration, fluid drawn in through vent 112 and driventhrough orifices 132 may efficiently dissipate heat from heat-generatingstructure 102. Because fluid impinges upon the heat-generating structurewith sufficient speed (e.g. at least thirty meters per second) and insome embodiments substantially normal to the heat-generating structure,the boundary layer of fluid at the heat-generating structure may bethinned and/or partially removed. Consequently, heat transfer betweenheat-generating structure 102 and the moving fluid is improved. Becausethe heat-generating structure is more efficiently cooled, thecorresponding integrated circuit may be run at higher speed and/or powerfor longer times. For example, if the heat-generating structurecorresponds to a high-speed processor, such a processor may be run forlonger times before throttling. Thus, performance of a device utilizingcooling system 100 may be improved. Further, cooling system 100 may be aMEMS device. Consequently, cooling systems 100 may be suitable for usein smaller and/or mobile devices, such as smart phones, other mobilephones, virtual reality headsets, tablets, two-in-one computers,wearables and handheld games, in which limited space is available.Performance of such devices may thus be improved. Because coolingelement 120 may be vibrated at frequencies of 15 kHz or more, users maynot hear any noise associated with actuation of cooling elements. Ifdriven at or near structural and/or acoustic resonant frequencies, thepower used in operating cooling systems may be significantly reduced.Cooling element 120 does not physically contact top plate 110 or orificeplate 130 during vibration. Thus, resonance of cooling element 120 maybe more readily maintained. More specifically, physical contact betweencooling element 120 and other structures disturbs the resonanceconditions for cooling element 120. Disturbing these conditions maydrive cooling element 120 out of resonance. Thus, additional power wouldneed to be used to maintain actuation of cooling element 120. Further,the flow of fluid driven by cooling element 120 may decrease. These,issues are avoided through the use of pressure differentials and fluidflow as discussed above. The benefits of improved, quiet cooling may beachieved with limited additional power. Further, out-of-phase vibrationof cooling element 120 allows the position of the center of mass ofcooling element 100 to remain more stable. Although a torque is exertedon cooling element 120, the force due to the motion of the center ofmass is reduced or eliminated. As a result, vibrations due to the motionof cooling element 120 may be reduced. Moreover, efficiency of coolingsystem 100 may be improved through the use of out-of-phase vibrationalmotion for the two sides of cooling element 120. For out-of-phasevibration of cantilevered arms 121, vibrations through cooling system100 may also be reduced. Consequently, performance of devicesincorporating the cooling system 100 may be improved. Further, coolingsystem 100 may be usable in other applications (e.g. with or withoutheat-generating structure 102) in which high fluid flows and/orvelocities are desired.

FIG. 1F depicts and embodiment of active cooling system 100′ including atop centrally anchored cooling element. Cooling system 100′ is analogousto cooling system 100. Consequently, analogous components have similarlabels. For example, cooling system 100′ is used in conjunction withheat-generating structure 102 and integrated circuit 103, which areanalogous to heat-generating structure 102 and integrated circuit 103.

Cooling system 100′ includes support structure 170′, top plate 110′having vents 112′, cooling element 120′, orifice plate 130 includingorifices 132, top chamber 140′ having a gap, bottom chamber 150 having agap and anchor 160 that are analogous to support structure 170, topplate 110 having vent 112, cooling element 120′, orifice plate 130including orifices 132, top chamber 140 having gap 142, bottom chamber150 having gap 152 and anchor 160, respectively, of FIGS. 1A-1E. Thus,cooling element 120′ is centrally supported by anchor 160 such that atleast a portion of the perimeter of cooling element 120′ is free tovibrate. In some embodiments, anchor 160 extends along the axis ofcooling element 120′ (e.g. in a manner analogous to anchor 360A and/or360B). In other embodiments, anchor 160 is only near the center portionof cooling element 120′ (e.g. analogous to anchor 360C and/or 360D).

Anchor 160 supports cooling element 120′ from above. Thus, coolingelement 120′ is suspended from anchor 160. Anchor 160 is suspended fromtop plate 110′. Top plate 110′ includes vent 113. Vents 112′ on thesides of anchor 160 provide a path for fluid to flow into sides ofchamber 140′.

Engineered cooling element 120′ has a tailored geometry and is usable ina cooling system such as cooling system 100 and/or 100′. Cooling element120′ includes an anchored region 122 and cantilevered arms 121′.Anchored region 122 is supported (e.g. held in place) in cooling system100 by anchor 160. Cantilevered arms 121′ undergo vibrational motion inresponse to cooling element 120′ being actuated. Thus, cooling element120′ operates in an analogous manner to cooling element 120 and can beused in cooling system 100. Each cantilevered arm 121′ includes stepregion 124, extension region 126 and outer region 128. In the embodimentshown in FIG. 1F, anchored region 122 is centrally located. Step region124 extends outward from anchored region 122. Extension region 126extends outward from step region 124. Outer region 128 extends outwardfrom extension region 126. In other embodiments, anchored region 122 maybe at one edge of the actuator and outer region 128 at the opposingedge. In such embodiments, the actuator is edge anchored.

Extension region 126 has a thickness (extension thickness) that is lessthan the thickness of step region 124 (step thickness) and less than thethickness of outer region 128 (outer thickness). Thus, extension region126 may be viewed as recessed. Extension region 126 may also be seen asproviding a larger bottom chamber 150. In some embodiments, the outerthickness of outer region 128 is the same as the step thickness of stepregion 124. In some embodiments, the outer thickness of outer region 128is different from the step thickness of step region 124. Outer region128 and step region 124 may each have a thickness of at least threehundred twenty micrometers and not more than three hundred and sixtymicrometers. In some embodiments, the outer thickness is at least fiftymicrometers and not more than two hundred micrometers greater than theextension thickness. Stated differently, the step (difference in stepthickness and extension thickness) is at least fifty micrometers and notmore than two hundred micrometers. In some embodiments, the outer step(difference in outer thickness and extension thickness) is at leastfifty micrometers and not more than two hundred micrometers. Outerregion 128 may have a width (from tip 123 to extension region 126) of atleast one hundred micrometers and not more than three hundredmicrometers. Extension 126 region has a length from the step region 124to outer region 128 of at least 0.5 millimeter and not more than 1.5millimeters in some embodiments. In some embodiments, outer region 128has a higher mass per unit length in the direction from anchored region122 than extension region 126. This difference in mass may be due to thelarger size of outer region 128, a difference in density betweenportions of cooling element 120′, and/or another mechanism.

As discussed above with respect to cooling system 100, cooling element120′ may be driven to vibrate at or near the structural resonantfrequency of cooling element 120′. Further, the structural resonantfrequency of cooling element 120′ may be configured to align with theacoustic resonance of the chamber 140′/150. The structural and acousticresonant frequencies are generally chosen to be in the ultrasonic range.For example, the vibrational motion of cooling element 120′ may be atthe frequencies described with respect to cooling system 100.Consequently, efficiency and flow rate may be enhanced. However, otherfrequencies may be used.

Cooling system 100′ operates in an analogous manner to cooling system100. Cooling system 100′ thus shares the benefits of cooling system 100.Thus, performance of a device employing cooling system 100′ may beimproved. The use of cooling element 120′ configured in a manneranalogous to cooling element 120′ may improve efficiency andreliability. In addition, vibrations in cooling system 100′ that mayaffect other cooling cells (not shown), may be reduced. For example,less vibration may be induced in top plate 110′ due to the motion ofcooling element 120′. Consequently, cross talk between cooling system100′ and other cooling systems (e.g. other cells) or other portions ofthe device incorporating cooling system 100′ may be reduced. Thus,performance may be enhanced.

Use of engineered cooling element 120′ may further improve efficiency ofcooling system 100 and/or 100′. Extension region 126 is thinner thanstep region 124 and outer region 128. This results in a cavity in thebottom of cooling element 120′ corresponding to extension region 126.The presence of this cavity aids in improving the efficiency of coolingsystem 100′. Each cantilevered arm 121′ vibrates towards top plate 110in an upstroke and away from top plate 110 in a downstroke. Whencantilevered arm 121′ moves toward top plate 110, higher pressure fluidin top chamber 140 resists the motion of cantilevered arm 121′.Furthermore, suction in bottom chamber 150 also resists the upwardmotion of cantilevered arm 121′ during the upstroke. In the downstrokeof cantilevered arm 121′, increased pressure in the bottom chamber 150and suction in top chamber 140 resist the downward motion ofcantilevered arm 121′. However, the presence of the cavity incantilevered arm 121′ corresponding to extension region 126 mitigatesthe suction in bottom chamber 150 during an upstroke. The cavity alsoreduces the increase in pressure in bottom chamber 150 during adownstroke. Because the suction and pressure increase are reduced inmagnitude, cantilevered arms 121′ may more readily move through thefluid. This may be achieved while substantially maintaining a higherpressure in top chamber 140, which drives the fluid flow through coolingsystem 100 and/or 100′. Moreover, the presence of outer region 128 mayimprove the ability of cantilevered arm 121′ to move through the fluidbeing driven through cooling system 100. Outer region 128 has a highermass per unit length and thus a higher momentum. Consequently, outerregion 128 may improve the ability of cantilevered arms 121′ to movethrough the fluid being driven through cooling system 100. The magnitudeof the deflection of cantilevered arm 121′ may also be increased. Thesebenefits may be achieved while maintaining the stiffness of cantileveredarms 121′ through the use of thicker step region 124. Further, thelarger thickness of outer region 128 may aid in pinching off flow at thebottom of a downstroke. Thus, the ability of cooling element 120′ toprovide a valve preventing backflow through orifices 132 may beimproved. Thus, performance of cooling system 100′ employing coolingelement 120′ may be improved.

As discussed above, cooling systems 100 and 100′ may coolheat-generating structure 102 (and thus integrated circuit 103) usingjets of fluid exiting orifices 132 and impinging on heat-generatingstructure (i.e. heat spreader) 102 or integrated circuit 103 (or anothercomponent that is a source of heat). However, cooling systems 100 and/or100′ may have an additional mechanism for cooling heat-generatingstructure. Cooling systems 100 and/or 100′ are thermally coupled toheat-generating structure 102 via support structure 170 such that heatmay be transferred from heat-generating structure 102 to cooling system100 via conduction. For example, pedestal 172 may be made from thermallyconductive materials. Pedestal 172 may also be joined to heat-generatingstructure 102 using a highly thermally conductive mechanism, such as athermally conductive epoxy. Similarly, pedestal 172 may have a thermalmass that is relatively large (e.g. a significant fraction of or greaterthan) compared to the thermal mass of heat-generating structure 102. Forexample, pedestal 172 may include or consist of high thermal capacitymaterial(s) (e.g. steels and aluminum alloys) and/or high thermalconductivity materials (e.g. copper and aluminum). Pedestal 172 may alsocontact heat-generating structure 102 over a wide area. Pedestal 172 mayrange in size from approximately the size of anchor 160 to across thecooling cell 100 and/or 100′ or across an entire tile formed of multiplecooling cells. For example, pedestal 172 may extend out of the plane ofthe page across the entire cooling system 100 or across multiple coolingsystems. Further, cooling element 120/120′ is thermally coupled tosupport structure 170 and/or 170′ via anchor 160 and/or top plate 110′,respectively. Thus, heat may be conducted from heat-generating structure102 to cooling element 120/120′ and the remainder of support structure170 and/or 170′, respectively. Thus, cooling system(s) 100 and/or 100′may act as heat sinks for heat-generating structure 102 and integratedcircuit 103. Further, because of its shape (e.g. large surface area),cooling element 120′ may function as a fin.

In addition, cooling system(s) 100 and/or 100′ are active coolingsystems. Consequently, cooling system(s) 100 and/or 100′ may beconsidered active heat sinks in some embodiments. More specifically,cooling element 120/120′ undergoes vibrational motion. In addition todriving fluid through orifices 132, the vibrational motion drives fluidinto chambers 140/150 and 140′/150, through chambers 140/150 and140′/150, and past cooling elements 120′. Because fluid is driven pastcooling element 120/120′ and through support structure(s) 170 and/or170′, heat in cooling element 120′ and support structure(s) 170 and/or170′ is transferred to the fluid. Consequently, in addition to orinstead of transferring fluid directly from heat-generating structure102, fluid can remove heat from cooling element 120/120′ and/or supportstructure 110/170′.

Moreover, cooling systems 100 and 100′ drive fluid such that fluidexiting orifices 132 has a high speed of at least thirty meters persecond. In some embodiments, the fluid exiting orifices 132 has a speedof at least forty-five meters per second. In some embodiments, the fluidexits orifices 132 at speeds of at least sixty meters per second. Otherspeeds may be possible in some embodiments. Fluid exiting orifices 132has a high speed in part because the fluid traveling through chambers140/150 has a high flow rate. In some embodiments, for example, the flowrate through chambers 140/150 may be at least 0.05 cubic feet per minute(cfm). In some embodiments, the flow rate through chambers 140/150 is atleast 0.1 cfm. Other (i.e. higher or lower) flow rates are possible. Therelatively high flow rates that may be driven through cooling system(s)100 and/or 100′ efficiently remove heat from cooling elements 120/120′and support structure(s) 170 and/or 170′. Thus, in addition toconduction by support structure 170/170′ and cooling element 120/120′,transfer of heat to the fluid via convection may be used to manage heat.

For example, FIGS. 2A-2G indicate the change in temperature of fluiddriven using cooling system(s) 100 and/or 100′. FIG. 2A is a graph 200depicting example of performance for cooling system(s) 100 and/or 100′.Graph 200 is for explanatory purposes only and not intended to representperformance of all embodiments of cooling element 120 and/or coolingsystem(s) 100 and/or 100′. More specifically, graph 200 depicts thetemperature of the fluid at various locations in cooling system(s) 100and/or 100′. Location “Vent” indicates the fluid temperature at theentry vent 112 and/or 113 to cooling system(s) 100 and/or 100′,respectively. Location “Orifice Exit” indicates the fluid temperatureafter exiting orifices 132 for cooling system(s) 100 and/or 100′,respectively. Location “Impingement” indicates the fluid temperatureafter impinging on heat-generating structure 102 for cooling system(s)100 and/or 100′, respectively. Location “Exit” indicates the fluidtemperature upon exiting the region shown for cooling system(s) 100and/or 100′, respectively. “Cap Temp.” indicates the temperature atwhich heat-generating structure 102 or integrated circuit 103 is desiredto remain below.

Graph 200 includes plot 210 that may be considered to describe high flowbehavior, while plot 220 can be considered to describe low flowbehavior. Plot 210 (high flow) may be for flows on the order of 0.1 cfmin some embodiments. Plot 220 (low flow) may be for flows on the orderof 0.01 cfm. Other flow rates are possible. More generally, plot 210 mayoccur where the flow of fluid driven by cooling element 120 and/or 120′through cooling systems 100 and/or 100′ is sufficient to cool portionsof cooling systems 100/100′ such that their temperatures aresignificantly less than that of heat-generating structure 102. Plot 220may occur where the flow of fluid driven by cooling element 120 and/or120′ through cooling systems 100 and/or 100′ is insufficient to coolportions of cooling systems 100/100′, such that their temperatures areclose to that of heat-generating structure 102. More specifically, plot210 indicates the behavior for cooling system(s) 100 and/or 100′ whenthe temperature of cooling system 100 and/or 100′ (e.g. the temperatureof cooling element 120 and support structure 170/170′) is well below thetemperature of heat-generating structure 102. For example, plot 210 maydescribe the temperatures when cooling system(s) 100 and/or 100′ are ator near room temperature (e.g. twenty-five degrees Celsius) whileheat-generating structure 102 and/or integrated circuit 103 are at ornear the cap temperature (e.g. ninety degrees Celsius). Plot 220indicates the behavior for cooling system(s) 100 and/or 100′ when thetemperature of cooling system 100 and/or 100′ (e.g. the temperature ofcooling element 120 and support structure 170/170′) is at or near thetemperature of heat-generating structure 102. For example, plot 220 maydescribe the temperatures when cooling system(s) 100 and/or 100′ are ator near eighty through eighty-eight degrees Celsius whileheat-generating structure 102 and/or integrated circuit are at or nearthe ninety degrees Celsius.

Cooling system(s) 100 and/or 100′ are being heated by heat thermallyconducted from heat-generating structure 102. For plot 210, fluidentering cooling system(s) 100 and/or 100′ at vent 112 and/or 113 is ator near room temperature. The rate of fluid flow is high (e.g. 0.05cfm-0.1 cfm or more). In some embodiments, the fluid flow issufficiently high that enough heat is removed from cooling system(s) 100and/or 100′ to ensure that the temperature(s) of portions of coolingsystem(s) 100 and/or 100′ distal from heat-generating structure are low.As the fluid travels through chambers 140/150 and/or 140′/150 due tovibrational motion of cooling element 120, some heat is transferred tothe fluid. In some embodiments, sufficient heat is transferred (removedfrom cooling system(s) 100 and/or 100′) to reduce the temperature ofsections of cooling systems(s) 100 and/or 100′ that are distal fromheat-generating structure 102. Fluid continues to remove heat fromcooling system(s) 100 and/or 100′ as the fluid transits the coolingsystem. Thus, the fluid increases gradually in temperature as the fluidpasses through chambers 140 and 150. The fluid impinging onheat-generating structure 102 transfers a significant amount of heatfrom heat-generating structure 102 to the fluid. Thus, the temperatureof the fluid has increased greatly at the “Impingement” location. Only asmall amount of additional heat might be removed as the fluid continuesto travel along the surface of heat-generating structure 102 to theexit. Thus, a significant amount of heat is transferred for the plot210, partly by removing heat from cooling system(s) 100 and/or 100′ andpartly by the fluid impinging on heat-generating structure 102. Forexample, in some embodiments, for a heat-generating structure operatingat ninety degrees Celsius, room temperature fluid entering vent 112/113may exit at a temperature of at least seventy degrees Celsius. For aheat-generating structure operating at ninety degrees Celsius, roomtemperature fluid entering vent 112/113 may exit at a temperature of atleast seventy-five to eighty degrees Celsius in some such embodiments.

For plot 220, fluid entering cooling system(s) 100 and/or 100′ at vent112 and/or 113 is at or near room temperature. However, the rate offluid flow is low. In some embodiments, the fluid flow is sufficientlylow that not enough heat is removed from cooling system(s) 100 and/or100′ to ensure that the temperature(s) of portions of cooling system(s)100 and/or 100′ distal from heat-generating structure are low. Heat fromheat-generating structure 102 and/or integrated circuit 103 (or otherheat source) has been transferred to cooling system 100 via thermalconduction. Heat from cooling system(s) 100 and/or 100′ (e.g. coolingelement 120 and/or support structure 170/170′) is transferred to thefluid as the fluid travels through chambers 140/150 and/or 140′/150 dueto vibrational motion of cooling element 120. Thus, the temperature ofthe fluid has increased greatly at the “Orifice Exit” location. Thefluid impinging on heat-generating structure 102 may transfer a smallamount of additional heat from heat-generating structure 102 to thefluid. Only a limited amount of additional heat might be removed as thefluid continues to travel to the exit. Thus, for the low flow plot 220,heat is transferred to the fluid primarily by the fluid passing throughcooling system(s) 100 and/or 100′. For example, in some embodiments, fora heat-generating structure operating at ninety degrees Celsius, roomtemperature fluid entering vent 112/113 may exit at a temperature of atleast seventy degrees Celsius. For a heat-generating structure operatingat ninety degrees Celsius, room temperature fluid entering vent 112/113may exit at a temperature of at least seventy-five to eighty degreesCelsius in some such embodiments.

As can be seen in plots 210 and 220 for cooling system(s) 100 and/or100′ at low temperature with respect to heat-generating structure 102(high flow) or for cooling system(s) 100 and/or 100′ at or near thetemperature of heat-generating structure 102 (low flow), a significantamount of heat may be transferred efficiently to the fluid. In addition,a significant amount of heat generated by integrated circuit 103 isremoved by the fluid. Thus, cooling system(s) 100 and/or 100′efficiently remove heat for both low and high flows. However, higherfluid flows may remove more heat per unit time and result in portions ofcooling system(s) 100 and/or 100′ being at a lower temperature.

The efficiency of cooling system(s) 100 and/or 100′ may also be seenmathematically. The amount of heat per unit time (H) transferred to afluid (which is then removed s the fluid exits the system) may be givenby:

H=(dm/dt)C _(p) ΔT

-   -   Where dm/dt is the mass flow for the fluid        -   C_(p) is the specific heat of the fluid        -   ΔT is the change in temperature of the fluid.

The change in temperature of the fluid can be broken down to:

ΔT=ΔT _(chamber) +ΔT _(Impingement) +ΔT _(jet channel)

-   -   Where ΔT_(chamber) is the change in fluid temperature through        chamber 140/150 or 140′/150        -   ΔT_(Impingement) is the change in fluid temperature due to            impingement on heat-generating structure 102        -   ΔT_(jet channel) is the change in fluid temperature as the            fluid travels in the jet channel

Thus, for the high flow case, most of the temperature change for thefluid occurs for ΔT_(Impingement). Thus, heat-generating structure 102may be rapidly cooled. For the low flow case, most of the temperaturechange for the fluid occurs for ΔT_(chamber). However, in either case,the fluid driven by cooling element 120 efficiently removes heatgenerated by integrated circuit 103 and/or heat-generating structure102. For example, in both cases, fluid entering at room temperature mayhave a temperature of at least seventy degrees Celsius when exiting thesystem. In some embodiments (e.g. for lower flows and/or higher heatgenerated), fluid entering at room temperature may have a temperature ofat least seventy-five degrees Celsius when exiting the system. In someembodiments, fluid entering at room temperature may have a temperatureof at least eighty degrees Celsius when exiting the system. This is incontrast to conventional systems utilizing conventional mechanisms (e.g.fans) for blowing fluid over a heat spreader in which fluid entering atroom temperature may have a temperature not exceeding forty or fiftydegrees Celsius. Thus, the large change in fluid temperature (e.g. onthe order of forty to fifty-five degrees Celsius or more) in someembodiments of cooling system(s) 100 and/or 100′ indicates that asignificantly larger amount of heat may be removed using coolingsystem(s) 100 and/or 100′.

The change in temperature of the fluid may also be seen in FIGS. 2B-2G.FIGS. 2B-2G depict cooling system 100 under various conditions. Forsimplicity, only top plate 110, cooling element 120, orifice plate 130,pedestal 172, and heat-generating structure 102 are labeled. In FIGS.2B-2G, heat-generating structure has the highest temperature. FIG. 2Bdepicts a heat map 230 for an embodiment of a cooling system which isnot thermally coupled via conduction to heat-generating structure 102 atlow flow (e.g. 0.015 cfm). For example, pedestal 172 connecting orificeplate 130 to heat-generating structure 102 may be thermally insulating.FIG. 2C depicts a heat map 240 for an embodiment of a cooling systemwhich is not thermally coupled via conduction to heat-generatingstructure 102 at higher flow (e.g. 0.1 cfm). As can be seen in heat map230 of FIG. 2B, some heat is transferred to cooling system 100, whilethe fluid well above top plate 110 remains cool. Thus, for low flow,some heat is transferred to cooling system 100, but is not significantlyremoved by the low fluid flow. Heat map 240 of FIG. 2C indicates thatthe higher fluid flow more efficiently removes heat from cooling system100. Thus, cooling system 100 is cooler. Fluid above cooling system 100is more consistently cool, including closer to cooling system 100.

FIG. 2D depicts heat map 250 for an embodiment of cooling system 100which is thermally coupled via conduction (e.g. through pedestal 172having a high thermal conductivity) to a heat-generating structure atlow flow (e.g. 0.015 cfm). FIG. 2E depicts a heat map 260 for anembodiment of a cooling system which is thermally coupled via conduction(e.g. through pedestal 172 having a high thermal conductivity) to aheat-generating structure at higher flow (e.g. 0.1 cfm). As can be seenin heat map 250 of FIG. 2D, a significant amount of heat is transferredto cooling system 100 via thermal conduction through pedestal 172. Thus,part of orifice plate 130 and cooling element 120 are close intemperature to heat-generating structure 102. Fluid near top plate 110has been heated somewhat, while the fluid well above top plate 110remains cool. Thus, for low flow, heat is transferred to cooling system100 via conduction, but is not significantly removed by the low fluidflow. Heat map 260 of FIG. 2E indicates that the higher fluid flow moreefficiently removes heat from cooling system 100. Thus, although heatwould be transferred via conduction (as indicated by heat map 250),cooling system 100 has been cooled by fluid flow. Thus, top plate 110,cooling element 120, most of orifice plate 130, and part of pedestal 172are lower in temperature in heat map 260 than in heat map 250.Consequently, heat is removed from heat-generating structure 102 viaconduction (to cooling system 100) and convection (from cooling system100 to fluid, which exits the region).

As can be seen in FIGS. 2B-2E, when thermally coupled to theheat-generating structure, heat may be transferred to the cooling system100/cooling element 120 via conduction. A flow through the coolingsystem 100, driven by vibrational motion of the cooling element, caneffectively remove heat from the cooling system and, therefore, from theheat-generating structure.

Similarly, FIGS. 2F and 2G depict heat maps 270 and 280, respectively,for an embodiment of a cooling system that is thermally coupled viaconduction to a heat-generating structure. FIG. 2F depicts a heat map270 for an embodiment of a cooling system which is thermally coupled viaconduction (e.g. through pedestal 172 having a high thermalconductivity) to a heat-generating structure at lower flow (e.g. 0.05cfm). FIG. 2G depicts a heat map 260 for an embodiment of a coolingsystem which is thermally coupled via conduction (e.g. through pedestal172 having a high thermal conductivity) to a heat-generating structureat higher flow (e.g. 0.1 cfm). As can be seen in FIGS. 2F-2G, whenthermally coupled to the heat-generating structure, heat may betransferred to the cooling system via conduction. Thus, pedestal 172 andlarger portions of orifice plate 130 and cooling element 120 are shownas having a higher temperature in heat map 270. In addition, heat map270 indicates that the highest temperature for cooling system 100 occurnear pedestal 172, which is thermally connected to heat-generatingstructure 102. Heat map 280 also indicates that the highest temperaturefor cooling system 100 occur near pedestal 172, which is thermallyconnected to heat-generating structure 102. However, portions of topplate 110, cooling element 120, and orifice plate 130 have been cooledby the higher flow. The lowest temperatures of structures 110, 120, and130 are in proximity to the higher flow. A flow through the coolingsystem, driven by vibrational motion of the cooling element, caneffectively remove heat from the cooling system and, therefore, from theheat-generating structure.

Thus, cooling system 100 and/or 100′ may efficiently remove significantamounts of heat generated while having a small size, having low profileand/or being low noise. Thus, performance of a variety of systemsemploying cooling system(s) 100 and/or 100′ may be improved.

FIGS. 3A-3D depict plan views of embodiments of cooling systems 300A,300B, 300C and 300D analogous to active cooling systems such as coolingsystem 100. FIGS. 3A-3D are not to scale. For simplicity, only portionsof cooling elements 320A, 320B, 320C and 320D and anchors 360A, 360B,360C and 360D, respectively, are shown. Cooling elements 320A, 320B,320C and 320D are analogous to cooling element 120. Thus, the sizesand/or materials used for cooling elements 320A, 320B, 320C and/or 320Dmay be analogous to those for cooling element 120. Anchors 360A, 360B,360C and 360D are analogous to anchor 160 and are indicated by dashedlines.

For cooling elements 320A and 320B, anchors 360A and 360B are centrallylocated and extend along a central axis of cooling elements 320A and320B, respectively. Thus, the cantilevered portions (i.e. cantileveredarms) that are actuated to vibrate are to the right and left of anchors360A and 360B. In some embodiments, cooling element(s) 320A and/or 320Bare continuous structures, two portions of which are actuated (e.g. thecantilevered portions outside of anchors 360A and 360B). In someembodiments, cooling element(s) 320A and/or 320B include separatecantilevered portions each of which is attached to the anchors 360A and360B, respectively, and actuated. Cantilevered portions of coolingelements 320A and 320B may thus be configured to vibrate in a manneranalogous to the wings of a butterfly (in-phase) or to a seesaw(out-of-phase). In FIGS. 3A and 3B, L is the length of the coolingelement, analogous to that depicted in FIGS. 1A-1F. Also in FIGS. 3A and3B, the depth, P, of cooling elements 320A and 320B is indicated.

Also shown by dotted lines in FIGS. 3A-3B are piezoelectric 323.Piezoelectric 223 is used to actuate cooling elements 320A and 320B.Although described in the context of a piezoelectric, another mechanismfor actuating cooling elements 360A and 360B can be utilized. Such othermechanisms may be at the locations of piezoelectric 323 or may belocated elsewhere. In cooling element 360A, piezoelectric 323 may beaffixed to cantilevered portions or may be integrated into coolingelement 320A. Further, although piezoelectric 323 is shown as havingparticular shapes and sizes in FIGS. 3A and 3B, other configurations maybe used.

In the embodiment shown in FIG. 3A, anchor 360A extends the entire depthof cooling element 320A. Thus, a portion of the perimeter of coolingelement 360A is pinned. The unpinned portions of the perimeter ofcooling element 360A are part of the cantilevered sections that undergovibrational motion. In other embodiments, anchor need not extend theentire length of the central axis. In such embodiments, the entireperimeter of the cooling element is unpinned. However, such a coolingelement still has cantilevered sections configured to vibrate in amanner described herein. For example, in FIG. 3B, anchor 360B does notextend to the perimeter of cooling element 320B. Thus, the perimeter ofcooling element 320B is unpinned. However, anchor 360B still extendsalong the central axis of cooling element 320B. Cooling element 320B isstill actuated such that cantilevered portions vibrate (e.g. analogousto the wings of a butterfly).

Although cooling element 320 A is depicted as rectangular, coolingelements may have another shape. In some embodiments, corners of coolingelement 320A may be rounded. Cooling element 320B of FIG. 3B has roundedcantilevered sections. Other shapes are possible. In the embodimentshown in FIG. 3B, anchor 360B is hollow and includes apertures 363. Insome embodiments, cooling element 320B has aperture(s) in the region ofanchor 360B. In some embodiments, cooling element 320B includes multipleportions such that aperture(s) exist in the region of anchor 360B. As aresult, fluid may be drawn through cooling element 320B and throughanchor 360B. Thus, cooling element 320B may be used in place of a topplate, such as top plate 110. In such embodiments, apertures in coolingelement 320B and apertures 363 may function in an analogous manner tovent 112. Further, although cooling elements 300A and 300B are depictedas being supported in a central region, in some embodiments, onecantilevered section of the cooling element 320A and/or 320B might beomitted. In such embodiments, cooling element 320A and/or 320B may beconsidered to be supported, or anchored, at or near one edge, while atleast part of at least the opposing edge is free to undergo vibrationalmotion. In some such embodiments, the cooling element 320A and/or 320Bmay include a single cantilevered section that undergoes vibrationalmotion.

FIGS. 3C-3D depict plan views of embodiments of cooling systems 300C and300D analogous to active cooling systems such as cooling system 100. Forsimplicity, only cooling elements 320C and 320D and anchors 360C and360D, respectively, are shown. Cooling elements 320C and 320D areanalogous to cooling element 120. Thus, the sizes and/or materials usedfor cooling elements 320C and/or 320D may be analogous to those forcooling element 120. Anchors 360A and 360D are analogous to anchor 160and are indicated by dashed lines.

For cooling elements 320C and 320D, anchors 360C and 360D, respectively,are limited to a central region of cooling elements 320C and 320D,respectively. Thus, the regions surrounding anchors 360C and 360Dundergo vibrational motion. Cooling elements 320C and 320D may thus beconfigured to vibrate in a manner analogous to a jellyfish or similar tothe opening/closing of an umbrella. In some embodiments, the entireperimeter of cooling elements 320C and 320D vibrate in phase (e.g. allmove up or down together). In other embodiments, portions of theperimeter of cooling elements 320C and 320D vibrate out of phase. InFIGS. 3C and 3D, L is the length (e.g. diameter) of the cooling element,analogous to that depicted in FIGS. 1A-1F. Although cooling elements320C and 320D are depicted as circular, cooling elements may haveanother shape. Further, a piezoelectric (not shown in FIGS. 3C-3D)and/or other mechanism may be used to drive the vibrational motion ofcooling elements 320C and 320D.

In the embodiment shown in FIG. 3D, the anchor 360D is hollow and hasapertures 363. In some embodiments, cooling element 320D has aperture(s)in the region of anchor D. In some embodiments, cooling element 320Dincludes multiple portions such that aperture(s) exist in the region ofanchor 360D. As a result, fluid may be drawn through cooling element320D and through anchor 360D. The fluid may exit through apertures 363.Thus, cooling element 320D may be used in place of a top plate, such astop plate 110. In such embodiments, apertures in cooling element 320Dand apertures 363 may function in an analogous manner to vent 112.

Cooling systems such as cooling system 100 and/or 100′ can utilizecooling element(s) 320A, 320B, 320C, 320D and/or analogous coolingelements. Such cooling systems may also share the benefits of coolingsystem 100100 and/or. Cooling systems using cooling element(s) 320A,320B, 320C, 320D and/or analogous cooling elements may more efficientlydrive fluid toward heat-generating structures at high speeds.Consequently, heat transfer between the heat-generating structure andthe moving fluid is improved. Because the heat-generating structure ismore efficiently cooled, the corresponding device may exhibit improvedoperation, such as running at higher speed and/or power for longertimes. Cooling systems employing cooling element(s) 320A, 320B, 320C,320D and/or analogous cooling elements may be suitable for use insmaller and/or mobile devices in which limited space is available.Performance of such devices may thus be improved. Because coolingelement(s) 320A, 320B, 320C, 320D and/or analogous cooling elements maybe vibrated at frequencies of 15 kHz or more, users may not hear anynoise associated with actuation of cooling elements. If driven at ornear the acoustic and/or structural resonance frequencies for thecooling element(s) 320A, 320B, 320C, 320D and/or analogous coolingelements, the power used in operating cooling systems may besignificantly reduced. Cooling element(s) S20A, 320B, 320C, 320D and/oranalogous cooling elements may not physically contact the plates duringuse, allowing resonance to be more readily maintained. The benefits ofimproved, quiet cooling may be achieved with limited additional power.Consequently, performance of devices incorporating the coolingelement(s) 320A, 320B, 320C, 320D and/or analogous cooling elements maybe improved.

FIG. 4 depicts an embodiment of active cooling systems 400 usable as anactive heat sink. FIG. 4 is not to scale. For simplicity, only portionsof cooling system 400 are shown. Cooling system 400 is analogous tocooling systems 100. Consequently, analogous components have similarlabels. For example, cooling system 400 is used in conjunction withintegrated circuit 503, which is analogous to integrated circuit 103.

Cooling system 400 includes cooling element 420 and support structure470 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 470 includes top plate 410 havingvent 412, orifice plate 430 including orifices 432, top chamber 440having a gap, bottom chamber 450 having a gap, anchor 460, and sidewalls474 that are analogous to top plate 110 having vent 112, cooling element120, orifice plate 130 including orifices 132, top chamber 140 havinggap 142, bottom chamber 150 having gap 152, anchor 160, and sidewalls174, respectively. Cooling element 420 is centrally supported by anchor460 such that at least a portion of the perimeter of cooling element 420is free to vibrate. In some embodiments, anchor 460 extends along theaxis of cooling element 420 (e.g. in a manner analogous to anchor 360Aand/or 360B). In other embodiments, anchor 460 is only near the centerportion of cooling element 420 (e.g. analogous to anchor 360C and/or360D). Cooling element 420 includes cantilevered arms 421, anchoredregion 422, and tip 423 that are analogous to cantilevered arms 121,anchored region 122, and tip 123, respectively. In some embodiments,cooling element 420 may be analogous to cooling element 120′. Supportstructure 470 also includes pedestal 472 analogous to pedestal 172.However, in the embodiment shown, pedestal 572 is integrated into a heatspreader or vapor chamber that is analogous to heat-generating structure102.

Sidewalls 474 also include apertures 476. In the embodiment shown,sidewalls 474 include apertures 476 and orifice plate 430 includesorifices 432. In some embodiments, orifice plate 430 is free of orificesor vice. Although orifices 476 are shown as oriented parallel to thesurface of orifice plate 430, in some embodiments, apertures 476 mayhave a different orientation. Apertures 476 allow for flow of fluidaround cooling element 420, but not past heat-generating structure 402.In cooling system 400, therefore, heat may be transferred fromheat-generating structure 402 to pedestal 472, cooling element 420 andother components of cooling system 400.

Also shown in FIG. 4 is an additional heat spreader 405 betweenheat-generating structure 402 and integrated circuit 403. Thus, coolingsystem need not be mounted directly to the component 403 that is thesource of heat. In other embodiments, heat spreader 405 may be omitted.

Cooling system 400 operates in an analogous manner to cooling system100. Cooling system 400 thus shares the benefits of cooling system 100.Thus, performance of a device employing cooling system 400 may beimproved. Because pedestal 472 has an integrated heat spreader, heat maybe more efficiently transferred from integrated circuit 403 to system400. Heat may then be removed by fluid driven through system 400 bycooling element 420. Thus, performance may be enhanced.

FIG. 5 depicts an embodiment of active cooling systems 500 usable as anactive heat sink. FIG. 5 is not to scale. For simplicity, only portionsof cooling system 500 are shown. Cooling system 500 is analogous tocooling systems 100. Consequently, analogous components have similarlabels. For example, cooling system 500 is used in conjunction withintegrated circuit 503, which is analogous to integrated circuit 103.

Cooling system 500 includes cooling element 520 and support structure570 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 570 includes top plate 510 havingvent 512, orifice plate 530 including orifices 532, top chamber 540having a gap, bottom chamber 550 having a gap, anchor 460, and sidewalls574 that are analogous to top plate 110 having vent 112, cooling element120, orifice plate 130 including orifices 132, top chamber 140 havinggap 142, bottom chamber 150 having gap 152, anchor 160, and sidewalls174, respectively. Cooling element 520 is centrally supported by anchor560 such that at least a portion of the perimeter of cooling element 520is free to vibrate. In some embodiments, anchor 560 extends along theaxis of cooling element 520 (e.g. in a manner analogous to anchor 360Aand/or 360B). In other embodiments, anchor 560 is only near the centerportion of cooling element 520 (e.g. analogous to anchor 360C and/or360D).

Support structure 570 also includes pedestal 572 analogous to pedestal172. However, in the embodiment shown, pedestal 572 is integrated into aheat spreader or vapor chamber that is analogous to heat-generatingstructure 102.

Cooling system 500 operates in an analogous manner to cooling system100. Cooling system 500 thus shares the benefits of cooling system 100.Thus, performance of a device employing cooling system 500 may beimproved. Because pedestal 572 has an integrated heat spreader, heat maybe more efficiently transferred from integrated circuit 503 to system500. Heat may then be removed by fluid driven through system 500 bycooling element 520. Thus, performance may be enhanced.

FIG. 6 depicts an embodiment of active cooling systems 600 usable as anactive heat sink. FIG. 6 is not to scale. For simplicity, only portionsof cooling system 600 are shown. Cooling system 600 is analogous tocooling systems 100 and/or 500. Consequently, analogous components havesimilar labels. For example, cooling system 600 is used in conjunctionwith integrated circuit 603, which is analogous to integrated circuit103.

Cooling system 600 includes cooling element 620 and support structure670 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 670 includes top plate 610 havingvent 612, orifice plate 630 including orifices 632, top chamber 640having a gap, bottom chamber 650 having a gap, anchor 660, and sidewalls674 that are analogous to top plate 110 having vent 112, cooling element120, orifice plate 130 including orifices 132, top chamber 140 havinggap 142, bottom chamber 150 having gap 152, anchor 160, and sidewalls174, respectively. Cooling element 620 is centrally supported by anchor660 such that at least a portion of the perimeter of cooling element 620is free to vibrate. In some embodiments, anchor 660 extends along theaxis of cooling element 620 (e.g. in a manner analogous to anchor 360Aand/or 360B). In other embodiments, anchor 660 is only near the centerportion of cooling element 620 (e.g. analogous to anchor 360C and/or360D).

Support structure 670 also includes pedestal 672 analogous to pedestal172. However, in the embodiment shown, pedestal 672 is thermally coupledvia conduction directly to integrated circuit 103.

Cooling system 600 operates in an analogous manner to cooling system100. Cooling system 600 thus shares the benefits of cooling system 100.Thus, performance of a device employing cooling system 600 may beimproved. Because pedestal 672 is directly thermally connected tointegrated circuit 603, heat may be more efficiently transferred fromintegrated circuit 603 to system 600 via conduction. Heat may then beremoved by fluid driven through cooling system 600 by cooling element620. Thus, performance may be enhanced.

FIG. 7 depicts an embodiment of active cooling systems 700 usable as anactive heat sink. FIG. 7 is not to scale. For simplicity, only portionsof cooling system 700 are shown. Cooling system 700 is analogous tocooling systems 100, 500 and/or 600. Consequently, analogous componentshave similar labels. For example, cooling system 700 is used inconjunction with integrated circuit 703, which is analogous tointegrated circuit 103.

Cooling system 700 includes cooling element 720 and support structure770 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 770 includes top plate 710 havingvent 712, bottom plate 730, top chamber 740 having a gap, bottom chamber750 having a gap, anchor 760, pedestal 772, and sidewalls 774 that areanalogous to top plate 110 having vent 112, cooling element 120, orificeplate 130, top chamber 140 having gap 142, bottom chamber 150 having gap152, anchor 160, pedestal 172, and sidewalls 174, respectively. Coolingelement 720 is centrally supported by anchor 760 such that at least aportion of the perimeter of cooling element 720 is free to vibrate. Insome embodiments, anchor 760 extends along the axis of cooling element720 (e.g. in a manner analogous to anchor 360A and/or 360B). In otherembodiments, anchor 760 is only near the center portion of coolingelement 720 (e.g. analogous to anchor 360C and/or 360D).

Bottom plate 730 is analogous to orifice plate 130, but has no orificestherein. Instead, orifices 732 in sidewalls 774 are shown. Thus, fluidis ejected in another direction than toward heat generating structure702. Therefore, cooling system 700 may not cool heat-generatingstructure 702 via impingement. However, cooling system 700 may stillcool heat-generating structure 702 and component 703. Thus, heat fromheat-generating structure 702 is transferred to cooling system 700 viaconduction through pedestal 722 and removed by the fluid in coolingsystem 700 driven by vibrational motion of cooling element 720.

Cooling system 700 operates in an analogous manner to cooling system100. Cooling system 700 thus shares the benefits of cooling system 100.Thus, performance of a device employing cooling system 700 may beimproved. For example, heat may be efficiently transferred atsteady-state behavior. Thus, performance may be enhanced.

FIG. 8 depicts an embodiment of active cooling systems 800 usable as anactive heat sink. FIG. 8 is not to scale. For simplicity, only portionsof cooling system 800 are shown. Cooling system 800 is analogous tocooling systems 100, 500, 600 and/or 700. Consequently, analogouscomponents have similar labels. For example, cooling system 800 is usedin conjunction with integrated circuit 803, which is analogous tointegrated circuit 803.

Cooling system 800 includes cooling element 820 and support structure870 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 870 includes top plate 810 havingvent 812, bottom plate 830, top chamber 840 having a gap, bottom chamber850 having a gap, anchor 860, and sidewalls 874 that are analogous totop plate 110 having vent 112, cooling element 120, orifice plate 130,top chamber 140 having gap 142, bottom chamber 150 having gap 152,anchor 160, and sidewalls 174, respectively. Cooling element 820 iscentrally supported by anchor 860 such that at least a portion of theperimeter of cooling element 820 is free to vibrate. In someembodiments, anchor 860 extends along the axis of cooling element 820(e.g. in a manner analogous to anchor 360A and/or 360B). In otherembodiments, anchor 860 is only near the center portion of coolingelement 820 (e.g. analogous to anchor 360C and/or 360D).

Cooling system 800 is most analogous to cooling system 700. Thus, bottomplate 830 is analogous to orifice plate 130, but has no orificestherein. Instead, orifices 832 in sidewalls 874 are shown. Thus, fluidis ejected in another direction than toward heat generating structure802. Therefore, cooling system 800 may not cool heat-generatingstructure 802 via impingement. Further, the pedestal has been removed.Thus, bottom plate 830 is directly connected to heat-generatingstructure 802. In some embodiments, heat-generating structure might beremoved, allowing bottom plate 830 to be directly coupled to integratedcircuit. Thus, heat from heat-generating structure 802 is transferred tocooling system 800 via conduction through bottom plate 830 and removedby the fluid in cooling system 800 driven by vibrational motion ofcooling element 820.

FIG. 9 depicts an embodiment of active cooling systems 900 usable as anactive heat sink. FIG. 9 is not to scale. For simplicity, only portionsof cooling system 900 are shown. Cooling system 900 is analogous tocooling systems 100, 500, 600, 700 and/or 800. Consequently, analogouscomponents have similar labels. For example, cooling system 900 is usedin conjunction with integrated circuit 803, which is analogous tointegrated circuit 903.

Cooling system 900 includes cooling element 920 and support structure970 analogous to cooling element 120 and support structure 170,respectively. Thus, support structure 970 includes top plate 910 havingvent 912, orifice plate 930 having orifices 932 therein, top chamber 940having a gap, bottom chamber 950 having a gap, anchor 960, pedestal 972,and sidewalls 974 that are analogous to top plate 110 having vent 112,cooling element 120, orifice plate 130 having orifices 132, top chamber140 having gap 142, bottom chamber 150 having gap 152, anchor 160,pedestal 172 and sidewalls 174, respectively. Cooling element 920 iscentrally supported by anchor 960 such that at least a portion of theperimeter of cooling element 920 is free to vibrate. In someembodiments, anchor 960 extends along the axis of cooling element 920(e.g. in a manner analogous to anchor 360A and/or 360B). In otherembodiments, anchor 960 is only near the center portion of coolingelement 920 (e.g. analogous to anchor 360C and/or 360D).

Orifice plate 930 does include orifices 932 (shown as dotted lines inFIG. 9 ). However, orifices 932 do not direct fluid to impinge onheat-generating structure 902. Thus, fluid is ejected in anotherdirection than toward heat generating structure 902. In the embodimentshown, fluid may be driven out of bottom chamber 950 in a directionsubstantially perpendicular to the plane of the page. Therefore, coolingsystem 900 may not cool heat-generating structure 902 via impingement.However, cooling system 900 may still cool heat-generating structure 902and component 903.

Various cooling systems 100, 100′, 400, 500, 600, 700, 800, and/or 900have been described and particular features highlighted. Variouscharacteristics of cooling systems 100, 100′, 400, 500, 600, 700, 800,and/or 900 can be combined in manners not explicitly depicted herein.

FIGS. 10A-10B depict an embodiment of active cooling system 1000including multiple cooling cells configured as a tile. FIG. 10A depictsa top view, while FIG. 10B depicts a side view. FIGS. 10A-10B are not toscale. Cooling system 1000 includes four cooling cells 1001, which areanalogous to one or more of cooling systems described herein, such ascooling systems 100 and/or 400. Although four cooling cells 1001 in a2×2 configuration are shown, in some embodiments another number and/oranother configuration of cooling cells 1001 might be employed. In theembodiment shown, cooling cells 1001 include shared top plate 1010having apertures 1012, cooling elements 1020, shared orifice plate 1030including orifices 1032, top chambers 1040, bottom chambers 1050,pedestals 1072, sidewalls 1074, and anchors 1060 that are analogous totop plate 110 having apertures 112, cooling element 120, orifice plate130 having orifices 132, top chamber 140, bottom chamber 150, pedestal172, sidewalls 174 and anchor 160. Although bottom anchors 1060 areshown, in other embodiments top anchors may be used. In the embodimentshown, cooling elements 1020 are driven out-of-phase (i.e. in a manneranalogous to a seesaw). Further, cooling element 1020 in one cell isdriven out-of-phase with cooling element(s) in adjacent cell(s).

Cooling cells 1001 of cooling system 1000 function in an analogousmanner to cooling system(s) 100 and/or 400. Consequently, the benefitsdescribed herein may be shared by cooling system 1000. Because coolingelements in nearby cells are driven out-of-phase, vibrations in coolingsystem 1000 may be reduced. Because multiple cooling cells 1001 areused, cooling system 1000 may enjoy enhanced cooling capabilities.

FIG. 11 depicts a top view of an embodiment of cooling system 1600including multiple cooling cells 1101. FIG. 11 is not to scale. Coolingcells 1101 are analogous one or more of the cooling systems describedherein, such as cooling systems 100 and/or 100′. As indicated in coolingsystem 1100, cooling cells 1101 may be arranged in a two-dimensionalarray of the desired size and configuration. In some embodiments,cooling system 1100 may be viewed as made up of multiple tiles 160.Thus, the desired cooling power and configuration may be achieved.

FIG. 12 is a flow chart depicting an exemplary embodiment of method 1200for operating a cooling system. Method 1200 may include steps that arenot depicted for simplicity. Method 1200 is described in the context ofpiezoelectric cooling system 100. However, method 1200 may be used withother cooling systems including but not limited to systems and cellsdescribed herein.

One or more of the cooling element(s) in a cooling system is actuated tovibrate, at 1202. At 1202, an electrical signal having the desiredfrequency is used to drive the cooling element(s). In some embodiments,the cooling elements are driven at or near structural and/or acousticresonant frequencies at 1202. The driving frequency may be 15 kHz orhigher. If multiple cooling elements are driven at 1202, the coolingelements may be driven out-of-phase. In some embodiments, the coolingelements are driven substantially at one hundred and eighty degrees outof phase. Further, in some embodiments, individual cooling elements aredriven out-of-phase. For example, different portions of a coolingelement may be driven to vibrate in opposite directions (i.e. analogousto a seesaw). In some embodiments, individual cooling elements may bedriven in-phase (i.e. analogous to a butterfly). In addition, the drivesignal may be provided to the anchor(s), the cooling element(s), or boththe anchor(s) and the cooling element(s). Further, the anchor may bedriven to bend and/or translate.

Feedback from the piezoelectric cooling element(s) is used to adjust thedriving current, at 1204. In some embodiments, the adjustment is used tomaintain the frequency at or near the acoustic and/or structuralresonant frequency/frequencies of the cooling element(s) and/or coolingsystem. Resonant frequency of a particular cooling element may drift,for example due to changes in temperature. Adjustments made at 1204allow the drift in resonant frequency to be accounted for.

For example, piezoelectric cooling element 120 may be driven at itsstructural resonant frequency/frequencies, at 1202. This resonantfrequency may also be at or near the acoustic resonant frequency for topchamber 140. This may be achieved by driving piezoelectric layer(s) inanchor 160 (not shown in FIGS. 1A-1F) and/or piezoelectric layer(s) incooling element 120. At 1204, feedback is used to maintain coolingelement 120 at resonance and, in some embodiments in which multiplecooling elements are driven, one hundred and eighty degrees out ofphase. Thus, the efficiency of cooling element 120 in driving fluid flowthrough cooling system 100 and onto heat-generating structure 102 may bemaintained. In some embodiments, 1204 includes sampling the currentthrough cooling element 120 and/or the current through anchor 160 andadjusting the current to maintain resonance and low input power.

Consequently, cooling systems, such as cooling system(s) 100, 100′, 400,500, 600, 700 800, and/or 900 may operate as described above. Method1200 thus provides for use of piezoelectric cooling systems describedherein. Thus, piezoelectric cooling systems may more efficiently andquietly cool semiconductor devices at lower power.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A system, comprising: a cooling element having afirst side and a second side opposite to the first side, the coolingelement being configured to undergo vibrational motion when actuated todrive a fluid from the first side to the second side; and a supportstructure thermally coupling the cooling element to a heat-generatingstructure via thermal conduction.
 2. The system of claim 1, wherein thesupport structure further includes: a bottom plate; and a plurality ofsidewalls forming a chamber therein, the cooling element residing in thechamber, at least one of the bottom plate and the plurality of sidewallshaving a plurality of orifices therein, the cooling element beingactuated to drive the fluid through the plurality of orifices.
 3. Thesystem of claim 2, wherein the vibrational motion drives the fluid suchthat the fluid exiting the plurality of orifices has a speed of at leastthirty meters per second.
 4. The system of claim 2, wherein the supportstructure further includes: a top plate having at least one venttherein, the cooling element being between the top plate and theheat-generating structure, forming a top chamber between the coolingelement and the top plate and a bottom chamber between the coolingelement and the bottom plate.
 5. The system of claim 1, wherein thecooling element has a central region and a perimeter, and wherein thesupport structure further includes: an anchor configured to support thecooling element at the central region, at least a portion of theperimeter being free to undergo the vibrational motion.
 6. The system ofclaim 1, further comprising: a heat spreader integrated with the supportstructure, the heat spreader being thermally coupled to the supportstructure and the heat-generating structure via thermal conduction. 7.The system of claim 6, wherein the support structure is configured suchthat the fluid exiting at least a portion of the plurality of orificesimpinges on the heat spreader to extract heat from the heat spreader,the heat spreader extracting heat from the heat-generating structure viathermal conduction.
 8. The system of claim 1, wherein the coolingelement is configured such that the fluid driven by the vibrationalmotion extracts heat from the cooling element.
 9. The system of claim 1,wherein the support structure further includes: a pedestal thermallyconductively coupled to the heat-generating structure.
 10. The system ofclaim 1, wherein the heat-generating structure is selected from anintegrated circuit, a battery, a heat spreader, and a vapor chamber. 11.An active heat sink, comprising: a plurality of cooling cells, each ofthe plurality of cooling cells including a cooling element, a top platehaving at least one vent therein, a bottom plate, a plurality ofsidewalls forming a chamber therein, and an anchor, the cooling elementresiding in the chamber between the top plate and the bottom plate, atleast one of the bottom plate and the plurality of sidewalls having aplurality of orifices therein, the cooling element being actuated toundergo vibrational motion to drive a fluid through the plurality oforifices; and a support structure integrated with the plurality ofcooling cells and thermally coupling the cooling element to aheat-generating structure via thermal conduction.
 12. The active heatsink of claim 11, wherein the cooling element has a central region and aperimeter, and wherein the support structure further includes: an anchorfor each of the plurality of cooling elements, the anchor beingconfigured to support the cooling element at the central region, atleast a portion of the perimeter being free to undergo the vibrationalmotion.
 13. The active heat sink of claim 11, further comprising: a heatspreader integrated with the support structure, the heat spreader beingthermally coupled to the support structure and the heat-generatingstructure via thermal conduction.
 14. The active heat sink of claim 11,wherein the cooling element is configured such that the fluid driven bythe vibrational motion extracts heat from the cooling element.
 15. Theactive heat sink of claim 11, wherein the support structure furtherincludes: a pedestal connecting the thermally conductively coupled tothe heat-generating structure.
 16. The active heat sink of claim 11,wherein the heat-generating structure is selected from an integratedcircuit, a battery, a heat spreader, and a vapor chamber.
 17. A methodof cooling a heat-generating structure, comprising: driving a coolingelement to induce a vibrational motion at a frequency, the coolingelement having a first side and a second side opposite to the firstside, the cooling element being configured to undergo vibrational motionwhen actuated to drive a fluid from the first side to the second side,the cooling element being thermally coupled by a support structure tothe heat-generating structure, the support structure thermally couplingthe cooling element to the heat-generating structure via thermalconduction.
 18. The method of claim 17, wherein the frequencycorresponds to a structural resonance for the cooling element andwherein the frequency also corresponds to an acoustic resonance for atleast a portion of a chamber in which the cooling element resides. 19.The method of claim 17, wherein the cooling element is one of aplurality of cooling elements and wherein the driving further includes:driving the plurality of cooling elements to induce the vibrationalmotion in each of the plurality of cooling elements, each of theplurality of cooling elements being thermally coupled to theheat-generating structure via thermal conduction.
 20. The method ofclaim 17, wherein a heat spreader is integrated with the supportstructure, the heat spreader being thermally coupled to theheat-generating structure.